investigation of the muon-induced background of the edelweiss-ii experiment

1 | Astrid Chantelauze | PhD defense | Université Blaise Pascal | 04/11/09

Investigation of the muon-induced background

of the EDELWEISS-II experiment

Astrid Chantelauze

KIT – Karlsruhe Institute of Technology

Université Blaise Pascal


Overview

Evidences of dark matter

Strategies of detection Direct detection: EDELWEISS-II experiment

Investigation of the muon-induced background: Muon veto performances Muon veto – bolometer coincidence analysis


Since 6 centuries…

Eppur si muove

Barred Spiral Milky Way Illustration, Credit: NASA/JPL-Caltech/R. Hurt (SSC)

Hello!


Rotation of spiral galaxiesUsing movement to measure mass

Vera Rubin (70s) showed that observation of rotation of disks in their outer parts required a lot of invisible mass …

E. Corbelli & P. Salucci MNRAS, 311, 441 (1999)

M33, Orange Observatory


Gravitational lensing

Galaxy Cluster Abell 2218

N. A. Bahcall et al., Astrophysical Journal, 447, L81(1995)

Image 1

Image 2

ObjectCluster

as seen by the observer

Observer

ΩM= 1

ΩM= 0.3


New order of the universe:

S. Perlmutter, Physics Today, 56, 53 (2003)

ΩΛ

Ωb

Ωnon-b

CDM

Ωtot = ΩΛ + ΩM + Ωk

ΩΛ

ΩM G. Hinshaw et al., Astrophysical Journal, 170, 288 (2007)

Ωk = 0.01 flat universe


New order of the universe: Ωtot = ΩΛ + ΩM + Ωk

S. Perlmutter, Physics Today, 56, 53 (2003)

ΩΛ

ΩM

Ωtot = ΩΛ + ΩM + Ωk = 1.011 ± 0.012

ΩΛ = 73 % (dark energy)

ΩM = 24 % (matter Ωb + Ωnon-b)

Ωb = 4 % (baryonic matter)

ΩDM = 20 % (dark matter)

ΩΛ

Ωb

Ωnon-b

CDM

8 | Astrid Chantelauze | PhD defense | Université Blaise Pascal | 04/11/09 as new unknown particles !

4%

20%


Dark Matter particle

4 main facts about its nature:

non-baryonic

weakly interacting

essentially stable, or at least have a life time long compared to the present age of the universe

cold = read slow-moving. More precisely, a cold dark matter candidate must be non-relativistic throughout the formation of largescale structure

freeze-out of a weakly interacting massive (WIMP) when reaction rate drops below expansion rate

time t (t ~ T-2)

increasing <Av>

thermodynamic equilibrium

E. W. Kolb & M. S. Turner, The Early Universe, Frontiers in Physics, Vol. 69 (1990)

x = m/ T

Tfreeze-out~ 1/20 · M


Galactic WIMP haloDark Matter in a cloud around the milky way

Lightest Supersymmetric Particle (LSP)

mass 50 GeV to ~ 1000 GeV

relative speed 270 km/s (~ our orbital velocity around galactic center)

in the same cup 60.000 ν

≈ 72 Ge

10-42cm2

0.3 GeV/cm3 (1 per cup)

only a few keV of recoil energy

very very rare scattering events (< 1 / week / kg)

200 cm³

cross section

local WIMP-density


ff needs astrophysical overdensities:

1. galactic center excess of cosmic rays (´s & antimatter)

2. the Sun energetic “solar” neutrinos (e, , )

3. the Earth “upward-going” muons from (, )

Dark Matter search

Indirect DM search ( annihilation)

Production at AcceleratorsHeavy strongly-interacting SUSY states (squarks, gluinos) produced copiously in p-p collisions

missing transverse momentum

Direct dark matterelastic scattering on a nucleus1. annual modulation2. event-by-event discrimination 72Ge


WIMP

Heat

Ionization

Light

Ge, CF3I, C4F10

liquid Xe/Ar

NaI, liquid.Xe

Ge, Si

CaWO4, BGO

Al2O3, LiF

…via elastic scattering off nuclei

1% energyfastestno surface effects

10% energy

100% energyslowestcryogenics

WIMP

Target

Edelweiss,CDMS

CRESST-2

Zeplin-3 , LUX,Xenon-10/100

DAMA, Libra, Zeplin-1,XMASS, KIMS, ANAIS

CRESST-1

CoGeNTCOUPPPicasso

WArP, ArDM

Direct DM search – detection schemes


EDELWEISS @ Laboratoire Souterrain de Modane

AltitudesDistances

1228 m 1298 m1263 m 0 m 6210 m 12 868 m

FRANCE ITALIE


Germanium bolometers

Simultaneous measurement Heat @ 17 mK with Ge/NTD thermometer Ionization @ few V/cm with Al electrodes

Evt by evt identification of the recoil by ratio Q = Eionization / Erecoil

Q = 1 for electronic recoil Q 0.3 for nuclear recoil

Guard ring

Center electrodem = 320g

NTD sensor

Heat

Ionisation

300

200

100

0

100

0

0 100 200 300 400 500

0 2 4 6 8 10t (ms)

t (ms)


n/ discrimination > 99.9% for Er >15 keV

73Ge(n,n’) 68.8 keV 13.3 keV

Ionization threshold 3.7 keV

Recoil threshold20 keV

calibration of a 320g Ge bolometer with 252CfStandard Q-plot

O. Martineau et al., NIM A, 530, 426 (2004)


The Edelweiss experiment

One Germanium detector

Some layers of detectors

The cryostat when it’s closed

The shielding of the experiment


42 modules covering 100 m2

98% coverage

energy, timing µ tracking capability

modular structure

read at both side

EDELWEIS-II muon veto system


“veto closed”

July 2006 – July 2009: 835.9 live days = 76%; 85% of data “closed”

Muon veto – Life timeposition known via laser meas.position known thanks to user

“veto open”


Muon candidates:

• Internal coincidence within a module

• strictly more than one module hit

• coincidence of two modules of different levels (module #4 and lower level)

Muon candidates


Muon rateGeant-4 simulationM.Horn, PhD thesis


Through going muons

expected time difference (vertical tracks):t = 5.2m / 3×108 m/s ≈ 17 ns

obtained from the fit: t ≈ 19 ± 2 ns

→ Δl = 5.7 ± 0.6 → non vertical but still “downward going muons”

High multiplicity events

→ showers


Coincidence analysis

Heat

Ioni

zatio

n /

Hea

t

removed !

Heat

Muon track

Region of interest for WIMP signals


Run 8 Run 10

running time 24/11/2007-18/03/2008 25/07/2008-24/11/2008 (17/08/2008-24/11-2008 for s3)

bometer system

number of bolometer 16 bolos = 16 Ge 14 bolos = 12 Ge + 2 ID (400g and 320g)

origin of data from flat files from ntp

rate 0.0146 Hz ~ 0.100 Hz per DAQ comp.

life time 285.4 kg.d 294.7 kg.d

veto system

number of modules all 42 modules ON all 42 modules ON

position of the veto chariots closed (logbook) chariots closed (laser meas.)

life time 98.8 days 84.3 days

rate 0.173 Hz 0.161 Hz

time stamp in 10µs from SC from OPERA BOX

independent per DAQ comp. unique for all subsystems

Coincidence analysis with Run 8


Run 8 – Distribution of the time

Time restarts with each run…

… perfectly continuous during a run

Connect correct veto period to run of s2 + same uncorrelated structure for other comput. → reconstrution of continuous a time line for all sub-systems

as viewed in the muon veto


Run 8 – Bolometer event building

∆tbolo > 500 ms


Muon veto-bolometers coincidences

∆tbolo > 500 ms

Define an interval attveto - tbolo = +25 ± 10 ms

> 1 veto module hit


> 1 veto module hitRun 8 – Systematics of the muon veto-bolometers coincidence interval

t = 25 ± 10 12.3 25.1 37.4

t = 25 ± 15 10.5 25.7 36.2

t = 20 ± 10 11.3 24.1 35.4

t = 20 ± 15 11.5 26.7 38.2

t = 23.45 ± 10

t = 23.5 ± 10

t = 23 ± 10

t = 24 ± 10

12.3 26.1 38.4

t = 23.5 ± 15

t = 23 ± 15

t = 24 ± 1510.2 26.2 36.4

coincidence interval for Run 8

tveto - tbolo in [+15, +35] ms

Time interval Low energy High energy Total excess

∆tbolo > 500 ms


> 1 veto module hitRun 8 – Coincidences at ER < 250 keV

2.9 ± 0.23.7 ± 0.2expected

accidentals

8.7 ± 2.43.3 ± 1.4signal/

background

25.1 ± 5.512.3 ± 4.2excess

coincidences

2816measured

events

Erecoil ≥ 250 keVErecoil < 250 keV

Muon-induced event rate: 0.04 events/kg.d

Erecoil < 250 keV

4 events at low Er, low Q:

(Er = 19 keV, Q = 0.26)(Er = 23 keV, Q = 0.17) (Er = 26 keV, Q = 0.23)(Er = 36 keV, Q = 0.31)

∆tbolo > 500 ms


Measured: 0.04 events/kg.d

Expected from Geant4 simulation: ~ 0.03 events/kg.d

Run 8 – Comparison with the simulation

Geant-4 simulationM.Horn, PhD thesis

hits

/cry

stal

(1/

keV

/da

y)

Energy deposit in bolometers/hit (keV)30

Compact geometry 120 bolometers 1 keV < Edep < 250 keV Multi hits

Erecoil < 250 keV

16 bolometers non compact 15 keV < Edep < 250 keV Single bolometer events


> 1 veto module hit


Erecoil ≥ 250 keV

Erecoil ≥ 250 keV

coincidences with ● multi(bolo) = 1■ multi(bolo) > 1

and if multi(bolo) > 1∆ individual bolometer

Run 8 – Coincidences at ER ≥ 250 keV

3 events at low Er, low Q:

(Er = 16 keV, Q = 0.22)(Er = 34.9 keV, Q = 0.47) (Er = 35 keV, Q = 0.33)

∆tbolo > 500 ms

33 | Astrid Chantelauze | PhD defense | Université Blaise Pascal | 04/11/09 Run 10Run 8


Characteristics of Run 8 and Run 10

Run 8 Run 10


bometer system





veto system




rate 0.173 Hz 0.161 Hz




New time stamp from the OPERA box

almost perfect

10-3 jumpsRemoving time mismatches:

as viewed in the muon veto



Run 8 Run 10


bometer system





veto system




rate 0.173 Hz 0.161 Hz




Run 10 - Events in the ntp file: Biplot heat vs ionization

s1

Events which pass the adaptative thresholdEvents which pass the adaptative threshold

Events which have ΣEH > 30 keV and ΣEI > 30 keV



Run 8 Run 10


bometer system





veto system




rate 0.173 Hz 0.161 Hz



0.0107 Hz


Run 10 – Bolometer event building

∆tbolo > 500 ms

Events with ΣEH > 30 keV and ΣEI > 30 keV


Run 10 – Muon veto-bolometers coincidences


∆tbolo > 500 ms

> 1 veto module hit

Define an interval attveto - tbolo = -5 ± 5 ms


Run 10 – Evaluation of the muon veto-bolometer coincidence interval

Time interval Low energy High energy Total excess

coincidence interval for Run 10

-5 ± 5 ms 4,4 28,6 32,9

-5 ± 10 ms 6,7 30,2 36,9

-5 ± 15 ms 7,1 28,8 35,9

-5 ± 20 ms 6,4 30,4 36,9

-0 ± 5 ms 3,3 22,6 25,9

-0 ± 10 ms 6,7 27,2 33,9

-0 ± 15 ms 7,1 31,8 38,9

-10 ± 5 ms 3,3 7,5 10,8

-10 ± 10 ms 4,7 30,2 34,9

tveto - tbolo in [-15, +5] ms


∆tbolo > 500 ms

> 1 veto module hit


Run 10 – Coincidences at EH < 250 keVQ

ualit

y of

coi

nci

den

t e

ven

ts

0 events at low EH, low Q ! Muon-induced event rate: 0.023 events/kg.d

Erecoil < 250 keV

Signal / Background = 2.4


∆tbolo > 500 ms

> 1 veto module hit



EHeat ≥ 250 keV

EHeat ≥ 250 keV

coincidences with ● multi(bolo) = 1■ multi(bolo) > 1

and if multi(bolo) > 1∆ individual bolometer

Run 10 – Coincidences at EH ≥ 250 keV

1 event at low EH, low Q:

(EH = 294,2 keV, Q = 0.41)

in coincidence with(EH = 151.1 keV, Q = 1.08)

Signal / Background = 9.1


∆tbolo > 500 ms

> 1 veto module hit


Summary

Muon veto allows to access the muon event topology (tracking in time and energy) and the muon flux

First combined analysis of both muon veto and bolometers

Identification of muon-induced events: ER< 50 keV …………. dominated by neutrons 50 < ER < 250 keV …. electron like single hits ER > 250 keV ……….. multi-bolometer events with single low-Q hits

Muon-induced events at ER<250 keV, for the EDW-II experiment: 0.04 events/kg.d

New EDW bolometer (ID) – e/ background free EURECA: joint effort of CRESST and EDW – 1 ton scale Non vetoed µ-induced bg would be the limiting background


Investigation of the muon induced background

of the EDELWEISS-II experiment

Astrid Chantelauze

KIT – Karlsruhe Institute of Technology

Université Blaise Pascal

46 | Astrid Chantelauze | IK-Institutsseminar | KIT | 17/11/09

25 ms

investigation of the muon-induced background of the edelweiss-ii experiment

Documents

matter b

cold dark matter candidate

galactic wimp halodark

new order

early universe

flat universe

muoninduced background

expansion ratetime t